1. Field of the Invention
The present invention relates to a test pattern for measuring the thickness of an insulating layer and a method for measuring a thickness of the insulating layer using the test pattern.
2. Description of the Related Art
It is often required to measure the thickness of an insulating layer form ed on wiring patterns of a semiconductor device.
It is known, in general, that the thickness of an insulating layer formed on wiring patterns varies between a region where wiring patterns are formed with high density and a region where only one wiring pattern is formed in an isolated manner after the planarization (Reference: Logic LSI Innovation, Science Forum Co. ltd., 1995, pp. 265-269). More specifically, it is known that the thickness of the insulating layer formed on wiring patterns arranged with high density is thicker than the insulating layer formed on an isolated wiring pattern, that is, a wiring pattern with low density. This is due to the difference in coating conditions of a coating layer (SOG layer) coated during flattening process.
Therefore, it is necessary to measure the thickness of an insulating layer which has been formed on wiring patterns and flattened by using planarization(flattering) technique, for example, when designing semiconductor device manufacturing process so as to know the uneven step coverage of a base.
As a method for measuring the thickness of an insulating layer formed on wiring patterns, there has been proposed a method using an optical measuring apparatus or using a capacitance measuring apparatus.
In the layer thickness measuring method by the optical measuring apparatus, light is applied to a target or an insulating layer to measure the layer thickness from the reflectance factor. In the method by the capacitance measuring apparatus, the capacitance of an insulating layer formed between an upper wiring pattern and a lower wiring pattern is measured after the flattening processing has been completed, to calculate the layer thickness based on the measurement value.
However, when the thickness of an insulating layer formed on wiring patterns is measured by using the above methods, there are the following problems.
In the method using these conventional measuring apparatus (such as an optical film thickness measuring apparatus and a capacitance measuring apparatus), if the surface area of a wiring member (conductive layer) forming wiring patterns is relatively large, the thickness of an insulating film on the wiring patterns can be measured at relatively high precision. On the other hand, if the thickness of an insulating film on fine wiring patterns where the surface area of a wiring member (a conductive layer) forming wiring patterns are small or the width of the wiring member (conductive layer) is narrow, then a measurement error becomes large and the film thickness cannot be measured at high precision.
Therefore, it is difficult to precisely measure the thickness of an insulating layer on wiring patterns in a region a fine wiring pattern arranged in an isolated manner, that is, arranged with low density. Accordingly, it is impossible to measure the thickness difference between a region where fine wiring patterns are arranged with high density and a region where a fine wiring pattern is arranged in an isolated manner.
It has been desired to measure the thickness of an insulating layer formed on wiring patterns even in a region where a fine wiring pattern is isolated, that is, arranged with low density.